No, Russian officials have not signed any such deal to deploy tactical nuclear weapons in Belarus.
Russia and Belarus have a close strategic alliance, and their armed forces often conduct joint military exercises designed to enhance cooperation. However, neither country has any nuclear weapons on their shared border and there have been no reports of any such agreement in play. Russia does maintain a small stockpile of tactical nuclear weapons which are currently stored at secure locations within its own borders for use if necessary, and has no reports of seeking to transfer them to Belarus.